Cardiac Action Potentials & Ion Movement
Flashcards covering resting membrane potential, the five phases of the ventricular action potential, and how ion movement produces EKG waveforms.
Keyboard Shortcuts
💡 Pro tip: Use keyboard shortcuts for faster studying!
Study Smart Tips for Cardiac Action Potentials & Ion Movement
Master these concepts using proven study techniques that actually work:
Active Recall
Test yourself before flipping each card to strengthen memory retention
Spaced Repetition
Review difficult cards more frequently than easy ones
Multiple Sessions
Break study time into shorter, focused sessions
Explain Aloud
Verbalize answers to reinforce understanding
Questions Covered in This Set
10 cards to master
What is the resting membrane potential of a ventricular myocyte?
About −90 mV, with the inside of the cell negative relative to the outside.
What does the Na⁺/K⁺ ATPase pump do?
Burns ATP to pump 3 Na⁺ out for every 2 K⁺ in, keeping Na⁺ high outside (~140 mM) and K⁺ high inside (~140 mM).
Why is the resting cell negative inside?
The membrane is leaky to K⁺ and nearly sealed to Na⁺, so K⁺ drifts out down its gradient, leaving unbalanced negative proteins and phosphates behind.
Write the Nernst equation for potassium and its resting value.
E_K = −61 × log₁₀([K⁺]in/[K⁺]out) ≈ −61 × log₁₀(140/4) ≈ −94 mV.
How does hyperkalemia (K⁺ = 7) change E_K, and what does it do to the EKG?
E_K rises to about −79 mV; the cell sits closer to threshold, Na⁺ channels partially inactivate, conduction slows — producing peaked T waves, then wide QRS, then a sine wave.
What happens in Phase 0, and what EKG wave does it create?
Fast voltage-gated Na⁺ channels open and Na⁺ floods in, driving the membrane from −90 to about +20 mV in 1–2 ms; across the ventricles this is the QRS complex.
What causes Phase 1 of the action potential?
Na⁺ channels inactivate and a transient outward K⁺ current (I_to) nudges the voltage slightly back down.
Describe Phase 2 (plateau) and its EKG correlate.
L-type Ca²⁺ channels let Ca²⁺ in, balancing K⁺ efflux, holding voltage near 0 mV for ~200 ms; Ca²⁺ triggers contraction and prevents tetany. On the EKG it is the flat ST segment.
What drives Phase 3, and which wave does it produce?
Ca²⁺ channels close and delayed rectifier K⁺ channels (I_Kr, I_Ks) let K⁺ pour out, returning voltage to −90 mV — recorded as the T wave.
Why is the T wave usually the same direction as the QRS?
Depolarization travels endocardium → epicardium, but repolarization begins at the epicardium; the two reversals cancel, making the T wave concordant with the QRS.
